Fiberglass tape hinge

dhbarr said:

ripstop by the roll will sell you a sample swatch, I almost guarantee.

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jqavins said:

It sounds like you were laying the wire on the balsa and gluing it there. If I've read it right, that means the glue joint is loaded in shear. In a shear joint like that, CA is just about the worst choice of glue. Also, any glue is likely to fail at holding a piece of music wire there, because there's so little contact area, so CA is doubly damned.

What you might try if you want to attach piano wire in that position is 1) bend a small loop in each end of the piece of wire. I realize that's easier said than done since the wire wants to spring back; it's not impossible. Then 2) use epoxy* to attach it. With any luck, the epoxy will key into the loops, giving you a compression loading. I can't guarantee it'll work; I'm brainstorming.

* While this is not a sheer load, where CA is at its worst, it's still not that great. In tension it shines, but otherwise it's just not "all that". I only use CA myself for temporary holding, like fin roots, before I can apply something better, like wood glue or epoxy fillets. I might use it for low stress joints if they're mainly in tension. And I use it for temporary hold that I want to be able to break apart.

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dhbarr said:

Shouldn't roughing the loops of the flats also help?

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Rktman said:

Roughing up the surface does help and I do, but the impact of the wings swinging up and coming to a dead stop is apparently too much for CA to handle. I'll be switching to epoxy.

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Rktman said:

My latest iteration uses duct tape but after seeing how it tends to stretch and open up the joint, I may have to resort to sewing the hinges as well. I was just concerned that getting the thread tight enough to close the hinge gap might hinder the opening of the wings at deployment?

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BABAR said:

As I said, this hinge is sewn in. It is not going to stretch.

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Rktman said:

I really like your original suggestion of using dental floss. I recently tried it as a burn string in place of cotton thread, and it absolutely doesn't stretch! Cotton, unfortunately, does, no matter how tightly it's initially pulled..

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BABAR said:

Interesting. For BURN strings (I am equating that to strings that hold the rocket components, including wings or rotors for gliders and copters, in closed position during boost phase, the string is burned through by ejection charge flame and releases the components hopefully at Apogee) I LOVE elastic thread BECAUSE it stretches. I can get enough tension on it that it KEEPS stuff in place due to the tension.

First, it is easy to get it tight in the first place (seems like no matter how tight you tie non-elastic thread, unless you do it like 10 seconds before launch it always gets a little lax over time, like between setup and walking it out to the pad.)

Second, once burned, it auto-retracts, it pulls itself away from the parts. This is why I have totally replaced burn strings with #16 rubber bands on my copters and airbrake recovery models, the bands hold the rotors closed, they hold the motors in place (both laterally, by closing the rotors in a case around the motor, AND in front of the motor they are in fact the motor stop that keeps the motor from shooting up through the rocket. Works great up to D size motors. They also loop around the rear of the motor on my motor eject models, keeps the motor from falling out the back during setup and boost). Added benefit that they come as a closed loop, I don’t even have to tie a knot! The two bands cross directly in front of the motor casing, perfectly lined up to melt in front of the ejection charge.

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BABAR said:

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Progress made.
Modified double tape hinge.
Uses Gorilla Brand duct tape. I am not normally a brand name guy, but this stuff is much stronger than regular duct tape and certainly better than the bargain basement brands and most of the brightly colored stuff, although I have used them and they DO work.

This keeps the cover piece on (10mm) so gap is completely covered on one side (we will call this the UP side.)

Instead of contiguous crossing strip on the down side, two narrow strips (5mm) run the full length. Nothing INSIDE THE GAP. I did run some thin CA along the gap balsa edges after the tape was on, before I sewed the hinges in.

Anyway, 4” wide hinge, essentially ZERO gap (when extended/flat, edges touch balsa to balsa on BOTTOM), this is as strong or stronger than the double tape hinge with cheaper duct tape. This puppy also is not going to stretch.

Does NOT quite flex as easily but pretty darn close.

1.2 grams.

Took me about 5 minutes to make.

For helicopter and air brake recovery rockets, this should be superb, the TOP side is a contiguous strip (no gap) so the drag should be LESS than just about anything else I have ever seen used as a hinge (I need to plan my “sewing” pattern better so the top surface runs orient forward/aft, that will cut down drag even more.)

For gliders, bottom side probably will mess up laminar flow a bit, even though it is balsa to balsa, but I think it is as good as anything else out there.

this COULD be done with thinner duct tape and probably would work for 10 or 20 flights. I don’t have many rockets I fly that many times, usually I have moved on to another version of something.

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BABAR said:

Wondered if anyone would catch that. Yes, the thread is in the gap, but if you tie it tight before you CA the thread, it is negligible. The same cannot be said for the gorilla tape.

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Rktman said:

I'll be doing another iteration of this flop wing glider and am considering using woven kevlar tape in place of duct tape. It's super thin (0.012"), really light, and extremely stretch resistant. Haven't decided whether to go with thinned epoxy or CA as an adhesive. Will sew it in with floss (or maybe kevlar thread) and soak it with thin CA. Will try not to overdo it with the adhesives as they can add a lot of weight. May have to substitute carbon fiber tube instead of spruce for the fuselage stick if the weight creeps up too much.

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